In a power generation using, e.g., a small-sized engine, a generator using a permanent magnet is used to generate alternating-current electricity. In this case, since the voltage thus generated is high or low depending on a rotational speed (RPM) of the engine, a shunt regulator is additionally used if necessary. However, when an output voltage is adjusted by the shunt regulator, a surplus power is always discharged as thermal energy, which leads to a waste of power. This wasteful control can be avoided by using an AC/DC converter. Japanese Patent Application Publication No. H01-148072 (JP H01-148072A) discloses an AC/DC converter for an AC input, which includes a rectifying circuit, a smoothing circuit, and a DC/DC converter.
In this regard, there may be employed an AC/DC converter that can be used as a regulator rectifier. Specifically, this is an AC/DC converter that receives an AC input generated by a generator using an engine rotation to obtain a stabilized DC output.
However, the conventional AC/DC converter has the following problems when it is used as the regulator rectifier.
In general, the regulator rectifier requires an input range from AC 0 V to AC 100 V or more, but, in this case, the load on the peripheral elements becomes large when a voltage control is performed only by a conventional PWM control. Therefore, there is a demand for an AC/DC converter which is suitable for a wide range of the input voltages.
In addition, a more stable output voltage is required to overcome a difficulty in achieving a desired control accuracy of the output voltage.
In view of the above, embodiments of the present disclosure provide a power supply device applicable as an AC/DC converter, which is configured to suitably respond to a wide range of input voltages and has a high output voltage accuracy.